A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF<sub>3</sub>)] studied with NMR and time-resolved IR spectroscopy

Ball, Graham E.; Brookes, Christopher M.; Cowan, Alexander J.; Darwish, Tamim A.; George, Michael W.; Kawanami, Hajime; Portius, Peter; Rourke, Jonathan P.

doi:10.1073/pnas.0610212104

Cited by 70 publications

(64 citation statements)

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“…Various research groups, including those of Ball and Duckett, have demonstrated that UV photolysis of samples within the NMR probe can be used to generate species that may then be characterised using conventional methods [88], while others have used photo-CIDNP to determine kinetic parameters [89,90]. Duckett and co-workers refined this approach to allow irradiation of the NMR tube using a 325 nm 25 mW He-Cd cw laser on pressurised samples at low temperature, initially using this method to study the reaction of CpRh(C 2 H 3 SiMe 3 ) 2 with parahydrogen [91].…”

Section: In Situ Photochemistry With Parahydrogenmentioning

confidence: 99%

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Duckett

Wood

2008

Coordination Chemistry Reviews

125

127

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Section: In Situ Photochemistry With Parahydrogenmentioning

confidence: 99%

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Duckett

Wood

2008

Coordination Chemistry Reviews

125

127

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“…We have carried out a TRIR study of both group 6 and 7 transition metal carbonyls in scCH 4 and liquid ethane (liqC 2 H 6 ). A related paper by Ball et al (34) in this issue reports an investigation on the photolysis of Re(Cp)(CO) 2 (PF 3 ) in higher alkanes by TRIR and NMR, which shows a delicate balance between the coordination and activation of the alkane. Here, we also observe a balance between the coordination and activation of CH 4 and C 2 H 6 after interaction with Re( 5 OC 5 R 5 )(CO) 2 fragments (R ϭ H or CH 3 ).…”

mentioning

confidence: 99%

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Cowan

Portius

Kawanami

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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We have used fast time-resolved infrared spectroscopy to characterize a series of organometallic methane and ethane complexes in solution at room temperature: W(CO)5(CH4) and M( 5 OC5R5)(CO)2(L) [where M ‫؍‬ Mn or Re, R ‫؍‬ H or CH3 (Re only); and L ‫؍‬ CH4 or C 2 H 6 ]. In all cases, the methane complexes are found to be short-lived and significantly more reactive than the analogous nheptane complexes. Re(Cp)(CO)2(CH4) and Re(Cp*)(CO)2(L) [Cp* ‫؍‬ 5 OC5(CH3)5 and L ‫؍‬ CH4, C2H6] were found to be in rapid equilibrium with the alkyl hydride complexes. In the presence of CO, both alkane and alkyl hydride complexes decay at the same rate. We have used picosecond time-resolved infrared spectroscopy to directly monitor the photolysis of Re(Cp*)(CO)3 in scCH4 and demonstrated that the initially generated Re(Cp*)(CO)2(CH4) forms an equilibrium mixture of Re(Cp*) ( T here is considerable interest in sigma-bonded organometallic alkane complexes, particularly since they have been identified as key intermediates in the transition metal-mediated COH activation process (1-3). Although such complexes generally are very short-lived intermediates (4), they have been known for over 30 years. Early experiments involved the photolysis of complexes such as Cr(CO) 6 and Fe(CO) 5 to generate the unstable intermediates Cr(CO) 5 or Fe(CO) 4 in low-temperature matrices, where coordination to cocondensed CH 4 results in the formation of Cr(CO) 5 (CH 4 ) and Fe(CO) 5 (CH 4 ) (5, 6).Flash photolysis experiments have demonstrated that the photolysis of Cr(CO) 6 in cyclohexane solution at room temperature forms Cr(CO) 5 (cyclohexane) (7). Subsequently, several examples of alkane complexes in solution have been reported, and studies on the mechanism of the COH activation process have clearly demonstrated the role of these complexes in oxidative addition reactions (1,8,9). Time-resolved infrared (TRIR) spectroscopy has proved to be a powerful tool for the study of metal carbonyl alkane complexes. Their reactivity decreases on going both across and down groups 5, 6, and 7 (10-12), and these observations led to the identification of a very long-lived alkane complex, Re(Cp)(CO) 2 (nheptane) (Cp ϭ 5 OC 5 H 5 ), which has a lifetime of Ϸ25 ms at room temperature (13). The relative stability of Re(Cp)(CO) 2 (alkane) complexes allowed Re(Cp)(CO) 2 (C 5 H 10 ) to be observed at 180 K by NMR spectroscopy (14), and subsequent NMR studies have been carried out to determine the binding modes of a series of related alkanes to the Re(CpЈ)(CO) 2 moiety (15, 16).The activation of methane is of particular interest because of the potential of using this abundant hydrocarbon as both an energy source and chemical feedstock (17). Organometallic methane complexes have been characterized in low-temperature matrix isolation experiments (5,6,18). In solution, the existence of methane complexes has been inferred by examining product ratios and from the rates of COH activation and reductive elimination reactions in isotopic labeling experiments (19).The lifetime of the...

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“…1a), forming a usually transient state known as a σ-complex 1,2 . Few σ-complexes have garnered as much attention as the σ-alkanes, putative intermediates in the catalytic C-H functionalization of alkanes, the pursuit of which has occupied researchers worldwide for decades [3][4][5][6][7] . A number of σ-alkane complexes have been characterized at low temperature by NMR, but the only structurally characterized examples are topics of debate 8,9 .…”

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Unsupported boron–carbon σ-coordination to platinum as an isolable snapshot of σ-bond activation

et al. 2012

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σ-Complexes of transition metals-key intermediates in metal-mediated bond activation and homogeneous catalysis-have traditionally been isolable only when chelating or when one of the participating atoms is hydrogen. Here, by treating the Lewis-basic transition metal complex [Pt(PEt 3 ) 4 ] with an electron-poor borirene, we isolate a complex with an unsupported borirene ligand bound, not through the unsaturated C = C bond, but exclusively via a B-C single bond. using nmR spectroscopy, X-ray crystallography and density functional theory calculations, we show, herein, that coordination of the borirene ligand is based on electron donation from the B-C σ bond to the metal, aided by a strong Pt-to-B dative interaction. The complex is the first isolable non-agostic σ-complex featuring two p-block elements and has broad implications as a model for the metal-mediated activation of strong p-block-p-block σ-bonds.

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A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF₃)] studied with NMR and time-resolved IR spectroscopy

Cited by 70 publications

References 24 publications

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Unsupported boron–carbon σ-coordination to platinum as an isolable snapshot of σ-bond activation

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A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF3)] studied with NMR and time-resolved IR spectroscopy

Cited by 70 publications

References 24 publications

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Parahydrogen-based NMR methods as a mechanistic probe in inorganic chemistry

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution

Unsupported boron–carbon σ-coordination to platinum as an isolable snapshot of σ-bond activation

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A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF₃)] studied with NMR and time-resolved IR spectroscopy